Daniel90

Hello,This is my first post here. After 7 years of searching I finally own a beautiful LHD '96 sl 500 with less than 70k Km, full optionals and in unreal conditions.
Everytime I drive there is a problem as seen in the video below.
- The engine loses 100 to 200 rpm
- it happens only while at constant speed
- it happens in 1500/2300 rpm range
- every 1 to 2 seconds, like a metronome
- I hear a slight noise/vibration coming from the right side, in the engine bay probably, while this happens.
- acceleration is always smooth/no other problems while driving
Other issues maybe related to the same problem:
- I noticed the car struggles to turn on. Starter motor goes long enough to think "oh god, the car won't start". Mostly when the engine is hot.

I think it's electrical because it's very precise.
I know it may be the OVP relay and I will check.
​​​​​Maybe I should also check some ECUs?

Here a brief video about the issue:
https://drive.google.com/file/d/1jrl0qibOuLwUQG5FmkHiczCwKGiF1pMX/view?usp=drivesdk

Thanks😃

AndreasHannover

I can't play the video but what you are describing is the torque converter lock-up clutch closing and then reopening, which is usually caused by worn out old automatic transmission fluid that has never been changed. It should be bright red, but it is probably dark brown like gravy.

mahunt

I know that color.

Daniel90

This video should work:
Please note that my foot was steady on the accelerator.

I will definitely check what you say, thanks!

I would also love to check the ECUs motherboard and the OVP relay.
They should be located in the right side of the engine bay, near the windscreen wipers.

I have a problem removing that black piece of plastic that prevents the access to the last 2 screws holding the cover.
Someone on this forum talked about this, but nobody told how to exactly do it. Besides, it seems not all the r129 are the same concerning ECU and OVP location!
Dan

AndreasHannover

Your R129 has no OVP Relais. It is the lock-up clutch.

Daniel90

Perfect!
I will check the ATF with my mechanic and update.